The aforementioned Provisional Application No. 60/199,532, U.S. application Ser. No. 09/505,017 for xe2x80x9cDigital Imaging System Utilizing Modulated Broadband Lightxe2x80x9d filed Feb. 16, 2000 by F. Hull, and U.S. application Ser. No. 09/484,405 for xe2x80x9cDigital Imaging System Utilizing Modulated Broadband Lightxe2x80x9d filed Jan. 14, 2000 by F. Hull are hereby incorporated by reference in their entirety and made a part of this application.
The present invention relates to a high resolution digital imaging device employing a non-coherent light source that is selectively modulated to create the individual pixels of the image to be recorded. The invention is particularly useful in the graphic arts industry for exposing a variety of light-sensitizable media such as printing plates, proofing materials, relief plates and the like.
In the graphic arts industry, high resolution images are formed by exposing a light-sensitizable medium such as a printing plate with an appropriate light pattern. Traditionally, the printing plates were covered with a patterned film and exposed by broadband light to create the desired image on the plate. The broadband light was utilized at low energy levels, such that the film intermediary was required to properly expose the plate. In this use the low level of energy strikes the entire area to be exposed for a fairly long time, 10 seconds to as much as 20 minutes, depending on the consumable.
More recently, methods that do not utilize film intermediaries have been developed. Such methods include utilizing digital laser imaging at much higher levels of energy. However, such laser devices employed with these methods are quite expensive due to the relatively high costs of lasers and of the special plates that operate with the laser imaging device, and the laser devices also operate at relatively low speeds. Attempts have also been made to implement printing devices capable of utilizing a broadband, non-coherent light source, with addressing of image pixels being accomplished by reflective spatial light modulators.
These devices have proved to be impracticable, in part due to the inability of the reflective spatial light modulators to withstand the required exposure to intense ultra-violet light, which rapidly breaks down the movable micro-mirrors of ferro-electric liquid of the modulators. The alternative is to employ a very fast and expensive media. There are a few varieties of modulators such as prism-type electro-optics, piezoelectric Kerr-cell and bi-morph piezoelectric combs that are capable of withstanding such energy. These modulators, however, are all based upon a line array as opposed to an area array. There are several patents, including U.S. Pat. No. 5,033,814 issued to Brown et al., that suggest the concept of using a DC short arc lamp, condensers and reflectors to illuminate a round bundle of fibers at one end, while the opposite end of the bundle of fibers are assembled in a straight line. There are several problems with this approach including light transmission efficiency, polishing of fibers and expense.
Additionally, the ultra-violet (actinic) radiation required to expose such graphic arts media has a wavelength in the range of 330 to 430 nano-meters, which further increases costs and reduces the overall efficiency when compared to the Brown et al. patent, which was not designed to deliver large amounts of power at these wavelengths.
It would therefore be a significant improvement in the art to provide a durable, high resolution digital imaging system utilizing a non-coherent light source, operable at high speeds with conventional printing plates. The requirements of such a light would include but not be limited to, the following: a stable illumination without an appreciable flicker; a nearly instant xe2x80x9conxe2x80x9d, minimizing a warm-up period; a high ratio of actinic radiation to total radiation; minimizing a xe2x80x9cripplexe2x80x9d component, caused by an AC power supply, interfering with modulation; evenly distributing illumination intensity over a specific area; providing an output spot nearly matching a modulator shape to eliminate the need for large fiber arrays; and providing a smaller and more uniform divergence angle in the illumination.